The longterm goals of this proposal are to provide an understanding in molecular terms of the interactions between sensitized lymphocytes, their products and macrophages which lead to the various manifestations of cell mediated immune reactions. The approach has been to use cloned, homogeneous macrophage-like cell lines, and use genetic selection techniques to obtain mutants or variants in vital macrophage function, thereby to understand the molecular mechanisms operative in normal macrophages. We have previously selected a variety of nonphagocytic macrophage variants selectively defective in their ability to endocytize through Fc-receptors, but are capable of non-specific phagocytosis of the inert particles. Some of the variants can be corrected to wild-type phenotype with cAMP. By pursuing the molecular mechanisms in one such variant, it has been possible to demonstrate that expression of Fc-receptors for IgG2a is controlled by cAMP, and Fc-receptor expression parallels endocytic capability. A second major project has been to explore cytocidal mechanisms of macrophages. We obtained a clone, J774.16 which upon appropriate stimulation produces a respiratory burst and O2 ions and H2O2. We have recently selected a variant which lacks the ability upon stimulation to produce O2 ions or H2O2 or oxidize glucose-1-14C. Experiments are underway to ascertain which types of parasites, bacteria and viruses require an oxidative cytocidal mechanism for killing by macrophages, to identify alternative cytocidal mechanisms, and to monoreconstitute the mutant with enzyme systems to define more precisely which oxygen metabolite is responsible for killing. Finally, we have been able to block EAE in vivo with inhibitors of macrophage-secreted proteases, indicating that they have a key role in tissue damage.